1. Field of the Invention
The present invention relates to a glass composition for various kinds of lamps such as a fluorescent lamp and an incandescent lamp, and a stem and a bulb for lamps that include the glass composition.
2. Description of the Prior Art
A glass composition for lamps is roughly divided into two groups. One is for stems including an exhaust tube and a flared base, and the other is for bulbs such as a luminescent bulb. In general, lead glass comprising 4 to 28 wt % of lead has been used for stems because it is handled easily in a forming process while heating. The glass bulb has been formed of a soda-lime silicate glass comprising 10 to 20 wt % of sodium oxide or about the same lead glass as for stems.
For environmental protection, cutting back on environmentally harmful materials is desired. In the field of lighting, problematic contaminants are lead and mercury. Lead is included in the glass for stems and bulbs. Therefore, some lead-free glass compositions have been proposed.
Tokkai-Hei 6-206737 discloses a glass composition free of PbO as well as toxic F, Sb2O3 and As2O3. The glass composition disclosed specifically, expressed in wt %, is e.g. SiO2: 68.0, Al2O3: 3.4, Li2O: 1.2, Na2O: 7.4, K2O: 5.0, BaO: 8.7, SrO: 2.9, MgO:1.3, CaO: 1.9 and SO2: 0.1.
Tokkai-Hei 9-12332 also discloses a glass composition free of PbO. In the glass composition, BaO is reduced because BaO tends to cause opacity of glass for stems, especially when used in a Danner method. The glass composition contains 0.3 to 3.5 wt % of BaO, and alkali metal oxides R2O (Rxe2x95x90Li, Na, K) than alkaline earth metal oxides Rxe2x80x2O (Rxe2x80x2xe2x95x90Mg, Ca, Sr, Ba) so as to keep shape-formability. The glass compositions disclosed specifically contains 15.5 to 16.0 wt % of R2O.
Tokkai-Hei 6-92677 also discloses a glass composition free of PbO. In the glass composition, TiO2 and CeO2 improve the solarization-resistant property and Fe2O3 increases the absorption of ultraviolet rays. In this glass composition, a predetermined amount of alkali metal oxide is considered necessary so as to suppress a rise of the softening point of the glass. The glass composition disclosed specifically contains at least about 15 wt % of R2O.
The glass compositions as described above can truly provide lead-free glass for lamps, but are not designed to reduce another environmentally affective material, mercury. At the present time, mercury is sealed into fluorescent lamps in more than a theoretically necessary amount for lighting because there is a necessity to consider the consumption of mercury by the glass while lighting.
Therefore, it is an object of the present invention to provide a glass composition for lamps that is substantially free of lead and can reduce mercury consumption, and a stem and a bulb for lamps that can meet the need of environmental protection.
An embodiment of the glass composition for lamps of the present invention consists essentially of the following constituents, expressed in percentages by weight:
and the total amount of Na2O, K2O and Li2O is not more than 13 weight %.
The glass composition provides glass for lamps that is substantially free of lead and has an advantage of suppressing the consumption of mercury in the lamps. In lighting, alkali ions such as sodium ions in the glass tend to diffuse, especially to move toward the inside of the bulb. Moving alkali ions facilitate the reaction of the alkali ions with mercury vapor and the fixation of mercury into the voids of the alkali ions. Mercury trapped in the voids no longer contributes to the electric discharge of the lamp. The glass composition of the present invention contains less R2O (Rxe2x95x90Li, Na, K) than conventional glass compositions. In addition, the glass composition contains diffusion inhibitors for alkali ions, e.g. BaO, in such an extent that the glass can be smoothly formed into a predetermined shape. Therefore, the glass composition can reduce the consumption of mercury.
Another embodiment of the glass composition for lamps of the present invention consists essentially of the following constituents, expressed in percentages by weight:
The glass composition also provides glass for lamps that is substantially free of lead and has an advantage of suppressing the consumption of mercury in the lamps. In particular, sodium oxide, which is considered to easily form an amalgam with mercury, is included in not more than 7 wt %. In this composition, the total amount of Na2O, K2O and Li2O is preferably not more than 13 wt %.
In one embodiment of the glass composition of the present invention, the total amount of Na2O, K2O and Li2O is preferably not more than the total amount of MgO, CaO, SrO and BaO.
The glass composition of the present invention is preferable in terms of environmental protection. The glass composition is determined by taking shape-formability in heating and other properties into consideration.
An embodiment of the stem and the bulb of the present invention includes glass having the glass composition of the present invention as described above. Thus, lamps that can meet the need of environmental protection are provided.